Figure 2.

Transmissive graphene phase shifters for dynamic wavefront shaping. (a) Transmission phase variation with biasing voltage and frequency in the hexagonal metallic metasurface integrated with graphene. The inset is a schematic of the structure. The dashed line at 350 V corresponds to the charge neutral point. At a fixed frequency 0.65 THz, dynamic phase shift of ${32}^{°}$ is observed by tuning the loss of graphene when V${}_g$ is from 350 V to −500 V. Reproduced with permission from [28], Copyright Springer Nature, 2012. (b) Unit cell of the hybrid metasurface consisting of a split-ring resonator and double-layer graphene capacitor. (c) Transmission magnitude and phase spectra at various biasing voltages. The dynamic phase shift is due to the tunable material loss of graphene. Reproduced with permission from [45], Copyright The authors, 2018. (d) Phase coverage and scattered magnetic field of uniform graphene ribbons by tuning the Fermi level. The phase coverage is limited to ${180}^{°}$. (e) Two parallel graphene ribbons are grouped in a unit cell to achieve nearly constant transmission intensity for different phase shifters. An array of such unit cells with individual biasing is simulated for anomalous refraction (top) and focusing with tunable focal length (bottom). Reproduced with permission from [46], Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2014.